This invention relates generally to measuring coating amount and, more specifically to measuring coating amount on metal surfaces.
Anodized coatings are created upon metallic substrates for a great variety of purposes. For example, aluminum aircraft parts often receive an anodized coating for corrosion resistance and for enhanced paint adhesion. Anodize coatings are also used for decorative purposes. Generally, a uniform coating amount or a coating amount within an acceptable range is desired. However, determining uniformity of the coating amount or quantifying the coating amount relative to a desired range may be difficult. Current coating amount testing methods are destructive and therefore cannot be used with final production products. They are also time consuming, environmentally unfriendly, and disruptive to large scale production processes. Anodize coating amount is sometimes specified for some applications and there is no simple non-destructive evaluation for measurement of anodize amount currently known in the art.
Current coating amount testing known in the art is performed by measuring the weight of a coated metallic test specimen. The coating is then chemically removed from the specimen. The metallic substrate is reweighed and the difference is the amount of the anodized coating, which is normally given in milligrams per square foot (mg/ft2). Because the test method is destructive, it cannot be used on the manufactured product. In addition, the currently known testing process only generates a spatially averaged coating amount for the sample. As such, the currently known testing process does not determine coating amount variations over an area.
Therefore, there exists an unmet need in the art for a nondestructive means of testing anodized coating amount on a metallic substrate.
The present invention provides a nondestructive method for efficiently determining the amount of an anodize coating formed upon a metallic substrate without stripping the anodize coating from the metallic substrate. The xe2x80x9camountxe2x80x9d of coating may represent either a coating thickness or weight. The invention may be employed in an in-line production facility or may be used intermittently as desired. The process may be used to provide a quantitative measurement, such as actual coating amount, or a qualitative measurement, such as a go or no-go result.
According to one embodiment of the invention, a non-destructive method is provided for determining the amount of an anodize coating on a metallic substrate. A value of infrared energy reflected from the metallic substrate without the anodize coating is determined. A value of infrared energy reflected from the metallic substrate with the anodize coating is determined. A value of infrared energy absorbed in the anodize coating is determined, and a value of the infrared energy absorbed in the anodize coating is correlated to an amount of the anodize coating.
According to an aspect of the invention, one embodiment of the invention includes transmitting an infrared beam having a predetermined wavelength through an anodize coating on a metallic substrate at a predetermined incident beam angle. The transmitted beam has a cross-sectioned area to produce a predetermined spot size on a surface of the anodize coating. The infrared beam is reflected off the metallic substrate to form a reflected beam and the reflected beam is filtered to a predetermined wavelength band, if desired, and detected. The infrared energy of the reflected beam is compared with a predetermined value of infrared energy reflected off the metallic substrate without the anodize coating to determine an absorbance value for the anodize coating. The absorbance value for the anodize coating is correlated to an amount of the anodize coating.